The invention relates to a method for the control and destruction of pathogenic microorganisms, in particular insects and worms, in an aquatic system, preferably for monitoring and controlling larvae. In a preferred fashion the invention relates to a method for controlling gnat/mosquito larvae in water bodies. Sustained reduction of microorganisms or destruction of their larvae is achieved by a two-step process in which chemical agents, such as insecticides, and biological agents are used in combination. Chemical agents specifically kill the larvae (e.g. mosquitoes) present in the aquatic system. Recolonization is prevented by zooplankton communities as biological agents which, according to the invention, preferably comprise food competitors of the microorganisms and larvae thereof. The combined use of chemical (insecticidal) and biological treatment in aquatic systems allows efficient and lasting control of insects and worms.
Numerous pathogenic microorganisms from the families of insects and worms are doing damage to humans, animals and plants. More specifically, the threat of insects, preferably mosquitoes, as carriers of disease (vectors) is increasing worldwide. This applies to tropical regions (Epstein, 1998), but also increasingly to temperate climates, for instance, the spread of Aedes albopictus in Italy since 1990 and its recent spread towards Germany (Knudsen et al., 1996). The out-breaks of Chikungunya fever in North-East Italy (Enserink, 2008) and the number of West Nile virus cases reported recently in USA and Europe (Balenghien, 2007) demonstrate the increasing relevance of vector-borne diseases to humans. As climate change and associated changes in weather (e.g., warming, rainfall patterns and resulting floods) are expected to continue, the problems associated with insects such as mosquitoes—and the diseases they transmit—are likely to increase in the future. Apart from mosquitoes, the schistosomiasis-causing larvae of schistosomes (trematodes), for example, likewise represent a major problem. There is thus an urgent need to develop effective methods of controlling such populations.
Thus, for example, mosquitoes live in two highly different habitats:                In the water: the eggs are laid here to develop larvae which feed on small organisms (such as algae, bacteria) in the water. The larvae pupate after several days of development. Finally, the adults (adult, winged animals) emerge from the pupae.        In the air and on land: the flying adult individuals hatch from the pupae and live outside the water.        
Mosquitoes are typical pioneer species (first species to colonize newly formed water bodies). For this reason, mosquitoes are frequently found in new or periodically drying water bodies, i.e., waters wherein few other species (e.g. those acting as competitors) are encountered.
As a rule, insecticides (chemical toxins) destroying the larvae are used in water bodies to reduce the larvae. The associated problems are well-known:    (1) Rapid recolonization by larvae: a short time after chemical treatment (a few days or a few weeks), new populations of larvae will form after oviposition of surviving insects.    (2) Stress on the ecosystem: chemical treatment may have strong effects on organisms other than insects. As a result, this may disturb the entire ecosystem being treated.    (3) Development of resistant insects: repeated chemical control treatment of populations frequently results in the development of resistance. As a consequence, the chemical effectiveness of control measures is reduced. In response, it is necessary to implement cost-intensive multiple treatments using higher concentrations.
The invention was therefore based on the object of developing a method for the control and destruction of pathogenic and/or troublesome insects and worms, which method no longer has the disadvantages of agents previously used, or only to a minor extent.